Control fleas using entomopathogenic nematodes

Fleas are one of the medically important pests of both animals and humans as they are capable of transmitting different kinds of disease causing organisms. Fleas are wingless insects but they can jump on their hosts including cats, dogs, humans and rats. Fleas have piercing and sucking type of mouthparts with that they suck blood of their hosts.  Like other insect, fleas also develop through the four different developmental stages including eggs, larva, pupa and adult.  Only adult fleas feed on blood but larval stage feeds on organic matter.  Pupa is a non-feeding stage. Fleas generally lay eggs on host’s body but they fall off on the ground where their host usually rests or sleeps.  Eggs hatch within 1-2 weeks and larvae immediately starts feeding on the organic matter that present at the resting place of animal hosts. Larvae develop through three larval stages and pupate in soil inside the silken cocoons. After 1-2 weeks, adult fleas emerge from cocoons but generally they use different kinds of host cues such as carbon dioxide, heat and vibration to emerge from pupae.  Fleas generally overwinter as larval and pupal stages, which can be easily targeted and killed by using biological control agents such as entomopathogenic nematodes.

Why now it’s time to apply entomopathogenic nematodes and reduce the existing populations and future outbreaks of fleas.

As we know that fleas overwinter as larval and pupal stages. In some places now temperature is already started declining, which is an important cue for fleas to get ready for winter weather.  This means both larval and pupal stages are ready for overwintering in the areas where temperatures are cooling down. Therefore, it is now time to apply entompopathogenic nematodes and target the overwintering stages of fleas.

Which species of entomopathogenic nematodes are effective against fleas?

• Steinernema carpocapsae nematodes are effective against fleas. It has been reported that when Steinernema carpocapsae nematodes applied in the potting medium, sand and gravel infested with larval and pupal stages of fleas, they reduced over 70% emergence of adults of cat fleas (Henderson et al., 1995).

Where to apply entomopathogenic nematodes for the effective control of outdoor and indoor fleas?

As stated above entomopathogenic nematodes can kill only larval and pupal stages but not adults of fleas. These stages are generally present on a large scale on the ground where host animals rests, sleeps or spends lot of time. These areas are generally located outdoors. These outdoor areas also serve as a source of indoor infestation of adult fleas. Therefore, it is important to treat all the outdoor animal resting/ sleeping areas or any other suspected areas where fleas are breeding with entomopathogenic nematodes.

When to apply entomopathogenic nematodes for the effective control of outdoor and indoor fleas?

• To target larvae and pupae of fleas, entomopathogenic nematodes should be applied starting from early spring through late fall i.e. when overwintering larval stages of fleas are becoming active and before emergence of adults from the pupae (spring and summer) or in the fall (September to November) when both larvae and pupae are getting ready for overwintering.
• Since nematodes are very sensitive to UV light, they will die within a minute or two when exposed to full sun. Therefore, nematodes should be applied early in the morning or late in the evening to avoid exposure to UV light.
• Another advantage of applying nematodes late in the evening is that the larval stages of fleas can be easily targeted because they are blind and do not like sunlight and therefore, they are generally active during night searching for food and easily found by entomopathogenic nematodes like Steinernema carpocapsae that uses sit and wait (ambush) strategy to attack its passing by host.  These nematodes can also find larvae and pupae that are hiding under organic matter during day time.

How many entomopathogenic nematodes should be applied for the effective control of fleas?

• See our Table for the exact quantity of Steinernema carpocapsae nematodes required to treat different square foot/meter areas.

How to apply entomopathogenic nematodes?

• Entomopathogenic nematodes that you receive in sponge as liquid formulation are thoroughly mixed in water and can be easily sprayed directly on the area where animal hosts rests/sleeps using traditional Knapsack/backpack sprayers or watering cans.
• However, at time of spraying care should be taken that the nematodes should not be allowed to settle at the bottom of sprayer or watering can to avoid their uneven distribution.
• To avoid the settling of nematodes at the bottom of sprayer or watering can, nematode suspension should be constantly agitated.
• However, nematodes will be easily damaged, if they are agitated through excessive recirculation of spray mix or if the temperature in the tank increases beyond 86^oF.
• Nematodes can also be applied through different types of irrigation systems but pumps should have proper pressure to avoid damage to nematodes and screen sizes should be larger than 50 mesh so that nematodes will pass through them live.
• Nematodes received in granular formulation can be directly applied by broadcasting with hand or for larger area by using traditional spreaders that are used for application of granular or pallet pesticides or synthetic fertilizers.
• Also, nematodes need about 20% moisture in the ground for survival. So please make sure nematode treated area should be watered immediately after the application of nematodes and continue to spray the area with water every few days.

[caption id="attachment_80" align="aligncenter" width="300" caption="Watering can for application of entomopathogenic nematodes on a small area"][/caption]

How Steinernema carpocapsae nematodes infect and kill fleas?

Infective juveniles of Steinernema carpocapsae enter their insect host through natural openings such as mouth, anus and spiracles and eventually reach in the insect body cavity, which is filled with the blood that is technically called as hemolymph.  The infective juveniles of Steinernema spp. carry in their gut species specific symbiotic bacteria of the genus, Xenorhabdus. Once infective juveniles of Steinernema spp. are in the insect body cavity, they release several cells of symbiotic bacteria, Xenorhabdus spp. from their gut via anus in the insect blood. Insect blood is conducive for the multiplication of symbiotic bacteria. In the blood, multiplying nematode-bacterium complex causes septicemia and kill their insect host usually within 48 h after infection.

Are entomopathogenic nematodes harmful to dogs, cats, chickens, birds, wild animals and humans?

• Entomopathogenic nematodes are absolutely not harmful to humans and any pet animals (dogs, cats, chickens and birds) and wild animals/birds, and even to beneficial insects like honeybees.

 Literature:

1. Henderson, G., Manweiler, S.A., Lawrence, W.J., Templeman, R.J. and Foil, L.D. 1995. The effects of Steinernema carpocapsae (Weiser) application to different life stages on adult emergence of the cat flea Ctenocephalides felis (Bouche). Vet. Dermatol. 6:159-163.
2. Smith, C.A. 1995: Current concepts: Searching for safe methods of flea control. JAVMA: 1137-1143.